It wasn't Cal she was running from but her whole class structure (which Cal represented as her future).

Jack was used to push Rose's boundaries. He gave her a chance to explore the world outside her strict social obligations (that were crushing her dreams).

Rose wasn't in love with Jack. Rose was in love with the idea that Jack represented to her.

The ideas of freedom and self determination. It was the understanding that her life was her own. Rose was not going to sacrifice her soul for appearances and the expectations of her mother. She had no choice. Escape or die.